The invention relates to a tube connecting mechanism which defines a longitudinal axis, and a connecting member. The connecting member includes a first bore starting from a planar end face of the connecting member. A nut is threadable onto the connecting member. The nut has a conical bore tapered away from the connecting member. A tube is guided through a bore of the nut. The tube includes a formation with two tensioning faces. The first tensioning face is supported on the connecting member in the tensioned condition of the tube connecting mechanism. The second tensioning face has a conical shape which corresponds to that of the conical bore of the nut and is supported in the conical bore of the nut.
Tube connectors are described in DD 240 059 A1. Here, the tube includes a connecting portion which is formed of the tube material and has contours of a standardized cutting ring. In consequence, the connecting member is provided with a conical bore having a 24.degree. cone. The nut has a conical bore with a 90.degree. cone in accordance with the standard. The cone angle of the first tensioning face, associated with the conical bore of the connecting member, is smaller than the cone angle of the conical bore of the connecting member. This achieves a linear contact of the first tensioning face at the smallest diameter of the conical bore. This measure is introduced to increase the sealing effect. The second tensioning face, which cooperates with the union nut, is pressed on. The conical piece starting from and running out forwardly towards the tube end is formed onto the second tensioning face by means of the first tensioning face. The disadvantage of such linear support is that due to the high axial threading forces, high surface pressures are generated which lead to settlement as a result of which the stringent sealing requirements are not permanently met. With cyclic bending loads introduced through the tube, the linear support of the tube in the connecting member also leads to settlement and, in consequence, to leakages.
U.S. Pat. No. 4,754,995 describes a similar tube connecting means. The tube has a fold whose first tensioning face constitutes a radius transition between a circular-cylindrical tube portion, arranged in front of the formation, and an inclined face of the union. The radius transition rests against a corresponding face in the connecting member. The face is provided in the form of a radius. The threaded-in nut has an end face which extends radially relative to the longitudinal axis. The nut rests against the second tensioning face. In this case, too, contact is established in the region of transition between the standard circular-cylindrical tube portion and the second portion of transition rounded towards the substantially radially extending part of the tensioning face. In addition, a cylindrical bore of the connecting member is provided with a recess accommodating a seal. The seal rests against the outer face of the cylindrical tube portion arranged in front of the formation.
This embodiment also leads to a disadvantage. When tightening the assembly, especially when repeating the tightening operation,,overtightening may occur because there is no firm, tangible stop indicating the final tightening stage of the connection.